1. Field
The embodiments described below relate to an interface device and a topology formation method.
2. Description of the Related Art
The amount of electronic devices installed in automobiles has drastically increased in recent years. Various functions have accordingly been added to automotive LANs. This has resulted in a demand for an automotive information LAN that operates at high-speeds and high-frequency bands so that high-quality digital videos and audio content can be enjoyed in automobiles. A standard referred to as 1394-Automotive, or IDB-1394, is now receiving attention as one solution to such an automotive information LAN that connects automotive multimedia devices.
The rapid progress of electronics in automobiles has resulted in the development of IDB-1394, which is an automotive serial interface based on IEEE-1394b. An IDB-1394 network has a high transmission frequency band to enable multiplex transmission of digital video streams and is suitable for an automotive multimedia network that performs multiplex transmission of video and audio data. An IDB-1394 information LAN enables high-quality digital contents of video provided by digital television (DTV) or DVD-Video and music provided by DVD-Audio to be appreciated in an automobile. This technology is also applicable to a rear-seat entertainment system, with which a video that differs from that watched in the front seat can be watched from the rear seat.
An IDB-1394 interface circuit is powered by a battery mounted on the automobile. To reduce power consumption of the interface circuit, when a bus cable is carrying no signals, an IDB-1394 circuit automatically shifts the ports connected to the bus cable to a low power consumption state (or a sleep state).
The IDB-1394 standard is based on the IEEE-1394b standard, which does not permit loop connections. With the IEEE-1394b standard, a loop test for detecting a loop connection is conducted. Japanese Laid-Open Patent Publication No. 2003-37613 describes the dissolving of a detected loop connection by, for example, logically disconnecting the final bus cable that has been connected to form the loop (bus cable 1c in the example of FIG. 1A). More specifically, the detected loop connection is changed to a daisy-chain connection by shifting a port P2B of a node 2 and a port P1C of a node 3 connected to the bus cable 1c to a Loop_disabled state, in which the ports P2B and P1C are logically disconnected.